MANILA, Philippines (AP) — A hole the size of a small car in the underside of a Qantas jumbo jet carrying 346 passengers forced the pilot to make an emergency landing Friday after a rapid descent over the South China Sea.

The Boeing 747-400 was cruising at 29,000 feet when a loud bang rattled the plane. Video shot by a passenger shows people sitting with their oxygen masks on as the jet descended quickly to 10,000 feet. Applause erupted as the plane touched down safely.

There were no injuries, but some passengers vomited after disembarking, said Octavio Lina, Manila International Airport Authority deputy manager for operations.

An official at the U.S. Transportation Security Administration, who spoke on condition of anonymity because the incident was not domestic, said initial reports show it was not related to terrorism.

"From the pictures coming in from Manila it's quite evident that a section of the fuselage gave way in flight," Jane's Aviation Expert Chris Yates said in a statement. "As a consequence of this the aircraft experienced rapid decompression. Fast action from the pilot and co-pilot ensured that all those aboard remained safe."

Investigators will now determine whether metal fatigue or manufacturing defect caused the panel to be ripped away from the remainder of the fuselage in flight, Yates said.

The aircraft appeared to be missing a plate of its metal skin at the joint where the front of the right wing attaches to the plane. A curved line of rivets was still visible on the body at the front edge where the sheet once was; a straight line of rivets is along the other.

Flight QF 30, from London to Melbourne, had just made a stopover in Hong Kong.

"One hour into the flight there was a big bang, then the plane started going down," passenger Marina Scaffidi, 39, from Melbourne, told The Associated Press by phone from Manila airport. "There was wind swirling around the plane and some condensation."

She said the hole extended from the cargo hold into the passenger cabin.

"No one was very hysterical," she said.

June Kane of Melbourne described how parts of the plane's interior broke apart in the depressurized cabin.

"There was a terrific boom and bits of wood and debris just flew forward into first (class) and the oxygen masks dropped down," she told Australia's ABC Radio. "It was absolutely terrifying, but I have to say everyone was very calm."

A report by the Manila International Airport Authority, quoting pilot John Francis Bartels, said the plane suffered an "explosive decompression." Australia's air-safety investigator said an initial investigation suggested "a section of the fuselage separated."

Lina said the cabin's floor gave way, exposing some of the cargo beneath and part of the ceiling collapsed.

"There is a big hole on the right side near the wing," he said, adding it was 7 1/2 feet to 9 feet in diameter.

Bob Vandel, executive vice president of the independent, Virginia-based Flight Safety Foundation, said the hole caused the plane to lose pressure and oxygen, which required the pilot to start a quick, initial descent to normalize oxygen levels, said Vandel.

"The plane lost pressure, so the pilot had to get the aircraft down below 12,000 feet pretty quickly," said Vandel.

The video shot by a passenger showed people sitting with their oxygen masks on — just-served meals on their tray tables. Cabin crew continued to work, walking down the aisles and showing no sign of panic.

Geoff Dixon, the chief executive officer of Qantas, praised the pilots and the rest of the 19-person crew for how they handled the incident.

"This was a highly unusual situation and our crew responded with the professionalism that Qantas is known for," he said.

Qantas — Australia's largest domestic and international airline — boasts a strong safety record and has never lost a jet to an accident, although there were crashes of smaller planes, the last in 1951. Since then, there have been no accident-related deaths on any Qantas jets.

However, the airline has had a few scares in recent years. In February 2008, a Qantas 717 with 84 passengers on board sustained substantial damage in a heavy landing in Darwin, Australia.

In addition, union engineers — who have held several strikes this year to demand pay raises — say that safety is being compromised by low wages and overtime work.

Qantas touts itself as the world's second-oldest airline, founded in 1920. As of December 2007, Qantas was operating 216 aircraft flying to 140 destinations in 37 countries, though in recent months it has announced it will retire some aircraft and cancel some routes — as well as cutting 1,500 jobs worldwide — due to skyrocketing fuel prices.

Late Friday, the passengers boarded another plane for Melbourne. The damaged plane was towed to a hangar in Manila.

Chief Superintendent Atilano Morada, head of the police Aviation Security Group, said his officers, including explosives experts, may assist in the airline's investigation.

"So far, they don't want us to touch it, so we will respect the aircraft owner. But we will make our personnel available if they need assistance in the investigation," he said.

The incident carried some echoes of a 1988 incident in which a large section of an older Aloha Airlines jetliner was torn off over Hawaii because of metal fatigue. Although the pilots were able to land, a flight attendant died and many of the 89 passengers were seriously injured.

Looks to me like a case of metal fatigue John, I'm definately no expert but I would imagine this particular area of the aircraft is a fairly stressed between the fuselage & wing as the amount of wing flex produced on these jumbo's must take a massive strain on the structure of the aircraft though they are well tested to extreme limits during the early days of the planes certification period. But time can take it's toll on everything eventually, but as you say disputes at the airline don't help. I wonder how old the aircraft was. Lucky enough they were no casualties anyway.

On closer examination at the hole it's remarkable that the whole aircraft was'nt ripped appart. Can you imagine the air been caught & sucked in to the particular area,especially when it had to go into a dive resulting in a higher speed. It has to be said that 747's are a surely a well built aircraft.

It is of course possible that such was identified on a different area of the airframe at an earlier date, and the necessary remedial action taken at the time.

It is certainly unlikely that an airline with the excellent reputation that Qantas enjoys would knowingly operate an aircraft on which untreated corrosion existed in a critical area. As always however, we shall have to await the outcome of the Investigation to discover the facts.

Don't know which Qantas incident you are referring to, but the following two come to mind.

Qantas did have a B747 overrun at Bangkok in 1999. The nose-gear collapsed but there was controversy at the time as to whether this caused the overrun, or occured during the the event itself.

In December 2007 it was discovered that Qantas Engineering at Melbourne International had, for some considerable time (reportedly 10 months), been replenishing aircraft Oxygen systems with Nitrogen. Apparently, the fittings on Oxygen and Nitrogen carts are different in order to prevent just such an occurrence. The Age newspaper reported at the time that, upon the introduction of what staff believed was a new Oxygen (but actually Nitrogen) cart the fittings from the old Oxygen cart were transferred to the new when it was discovered that the originals were not compatible with aircraft Oxygen systems.

The link I gave refers to a total loss of electrical power during the last 15 minutes or so of an LHR-SYD flight that was stopping over at BKK in Jan 2008. The reason I remember that one is that my sister was on that flight a few days earlier. Apparently, it was caused by a water leak in an area where there shouldn't have been one.

The Incident, which occurred last January, referred to a Qantas B747-400 ex London whilst making and intermediate stop at Bangkok.

During the descent the Cabin Crew reported a water leak in the forward galley. This was shortly followed by loss of power from three of the four AC buses, automatic disengagement of auto-throttle and autopilot, and blanking of the First Officer's displays. The Captain's flight and navigation displays, although degraded, were still available, as were standby instruments. The aircraft landed safely.

Investigation showed that the fibreglass drip-shield under the forward galley, designed to prevent fluids from reaching the main avionics centre located directly below it, was cracked. Subsequent inspection of the 30 B747s in the Qantas fleet revealed that 14 had cracked drip-trays.

A heating element designed to prevent icing of the external water drain hose arrangement was also found to be unserviceable, and the drain-hose itself was split. It was reported that inspection of the other B747s in the fleet showed six had unserviceable drain heater elements and two had split drain-hoses.

Expert opinion is that it was indeed fortuitous that the Incident occurred over land, and within 15 minutes of destination. Had it occurred on a long over-water flight, when the relatively short life of the battery standby system would have become a factor, then the outcome might have been somewhat less fortunate.